Recollection of hilly Rome maybe coming back (6)
I believe the answer is:
memory
'recollection' is the definition.
(I've seen this before)
'of hilly rome maybe coming back' is the wordplay.
'of' indicates the answer is hidden within the clue.
'coming back' shows that the letters should be reversed in order.
'yromem' is hidden within 'hilly rome maybe'.
'yromem' in reverse letter order is 'MEMORY'.
(Other definitions for memory that I've seen before include "Something remembered" , "Faculty of recall" , "honour?" , "Reminiscence" , "Mental retention" .)